A general purpose information transfer system such as employed aboard naval vessels, for example, functions to provide point-to-point analog or digital signal information. Such a system may employ multiplexing, common data bus techniques, and coding for the interchange of signal information.
In such a system, multiple multiplexes and data buses may be employed with a plurality of carrier frequencies so that multiple separate messages may be transmitted simultaneously. When such a system is electrically implemented, it is subject to severe interference problems due primarily to electromagnetically noisy environment of a typical naval vessel.
Such problems and disadvantages can be largely obviated by the employment of optical signal transmission using fiber optic cables and electro-optical transducers, such as photodiodes and light emitting diodes, for example. However, the transmission of signal information over optical data buses incurs significant attenuation of the optical signal strength. One expedient is to increase the initial optical signal strength to sufficiently overcome the effects of long line optical data transmission. In such optical information transfer systems, however, there are frequently included a multiple number of taps on an optical data bus line, each of which incurs a degree of attenuation, apart from the attenuation incurred by reason of transmission along the data bus itself.
As the number of such taps on an optical data bus increases, a point is reached where the end-to-end loss exceeds the capability of the transmission-receiver combination overcome it. When this point is reached, additional gain of signal strength is required between the end couplers in order that the length of the optical data bus may be extended to provide a full and adequate system.
An amplifier assembly arranged to provide the required optical signal amplification is customarily referred to as an active device or repeater-amplifier. Though such optical signal amplifier assemblies are widely employed in optical information transfer systems, one basic objection to their inclusion in otherwise passive optical signal information systems is that the overall system reliability is decreased due to the fact that the failure of a single series-connected repeater-amplifier or its power source will render an entire optical bus inoperative.
It is therefore desirable that a fail-safe optical repeater-amplifier assembly be devised for use in an optical data bus arrangement so that the failure of such repeater-amplifier and/or its power source will not render the optical bus entirely and completely inoperative.